The link you give confirms that the video bitrate alone is >5 Mb/s for 720p. More than 10 into 10 does not fit I'm afraid.
There's nothing like empirical data...
I just started playing "Ripper Street" in HD on our YouView box, and watched the traffic statistics accumulate on DslStats - which is reading the throughput data from the modem/router.
Before playing: throughput was around 2,000 kB/min
While playing: throughput at minimum was 30,000 kB/min, peak 45,000kB/min, average around 40,000kB/min.
It looks like the iPlayer stream ends up averaging around 38,000 kB/min ... or a hair over 5Mbps.
But it seems to be impossible to get the STB to tell me what kind of streams it has chosen for me.